1. Field of the Invention
The invention relates to technology of displaying a map image on a display screen.
2. Description of Related Art
A navigation device may include a map image display device that displays a map image in which structures are stereographically depicted. A stereographic map image serves to offer improved visibility to a user. Since there are many structures in urban areas or the like, in a case where all of the structures are displayed under the same conditions, visibility may deteriorate. Japanese Unexamined Patent Application Publication No. 2006-317764 (JP 2006-317764A) proposes technology of reducing deterioration of visibility by emphasizing structures in different degrees which are contained in the a displayed map image. The technology proposed in JP 2006-317764A determines a structure to be emphasized based on the fact that a human is likely to pay attention to nearby structures but particularly, is unlikely to pay attention to distant and small structures. Specifically, multiple structures are determined and displayed such that a structure closer to a reference position and higher than other structures is emphasized (refer to second to seventh paragraphs and the like in JP 2006-317764A).
The density of structures is high, and there are many high-rise structures in urban areas of a large city. For this reason, even if a structure to be displayed in an emphasized manner is selected based on the distance to the reference position or the height of the structure, a large number of structures may become selection targets. As a result, the structures may not serve as landmarks, and convenience may be decreased.